Abstract : Giant axons of the Chilean squid were used to study: (a) enzyme systems of isolated membrane fragments as the cation-activated ATPase system and electron transfer reactions; (b) the ability to transport sodium against an electrochemical gradient in perfused giants axons; (c) filtration coefficient of axon membrane as measured by hydrostatic and osmotic methods. Results gave information of the biochemical processes of nerve membranes, which can be studied in vivo, using intracellular perfused axons. However it was not possible to find the conditions to restore simultaneously the active transport of sodium, the bioelectric properties and the operation of the biochemical reactions studied in vitro. Measurements of hydraulic conductivity of nerve membrane by hydrostatic and osmotic methods suggest the presence of heterogeneity in pore distribution in the axon membrane. (Author)